VCE Environmental Science Unit 3: Biodiversity Measuring Biodiversity
Biological Sampling• The study of any species requires an estimate of their density in different habitats. Scientists use many different methods of measuring density, depending on the size, abundance, behaviour and habitat of the species. Sometimes a line transect and quadrats are used to measure the abundance and cover of different floral species in a grassland reserve.• Reference: Charles J. Krebs (1985) “Ecology – The Experimental Analysis of Distribution and Abundance” Harper International, New York.
Sampling techniques:• Aerial photographs (eg. whales, herds of moose or other hoofed mammals during migration, flamingos)• Capture-recapture (or mark and release)• Traps (eg. Elliot traps for small mammals, pit-fall traps for reptiles, light traps for insects, harp traps for bats)• Number of fecal pellets• Vocalisation frequency• Pelt records• Catch per unit fishing effort• Number of artifacts (nests, pupal cases, burrows etc.)• Questionnaires (of hunters and trappers for example)• Cover (of plants)• Feeding capacity (amount of bait taken)• Roadside counts• Bird surveys (OBP and red-tailed black cockatoos)
Aerial photographs are suitable for largemammals that congregate in knownlocations.
Brush-tailed Rock Wallaby – Critically Endangered
Biological Sampling• Each method has it’s advantages and disadvantages and is most valuable when used as an adjunct to more direct methods. This article from the CSIRO, “Estimating whale numbers in the Southern Ocean” explains how scientists go about estimating the abundance and population structure of minke whales.• This activity, Counting Smarties, from Maths by Email, models the “Mark and Recapture” or “Tag and Release” methods using smarties.
Species Site A Site BShrub 1 3 1Shrub 2 7 2Understorey 1 5 0Understorey 2 6 2Understorey 3 94 94Understorey 4 75 75Weed 1 0 2Weed 2 0 20D = 1 – p2 0.5961 0.6129
Simpson’s Index• Simpsons Diversity Index (D) is a measure of diversity. In ecology, it is often used to quantify the biodiversity of a habitat. It takes into account the number of species present, as well as the abundance of each species.• This index is based upon the probability that two specimens belong to the same species.• It ranges from 0 (low diversity) to 0.9999 (high diversity)
Simpson’s IndexPage 49 (1st ed) Page 53 (2nd ed)Calculate the ‘p’ value = no. of individuals Total Number Calculate p2 (site A)= p x p = 0.4039 Simpson’s Index (D) = 1-0.4039= 0.5961 Calculate p2 (site B) = p x p = 0.3871 Simpson’s Index (D) = 1 – 0.38712= 0.6129
Discussion Questions:• Describe the species diversity before and after sheep grazing• What does the calculated Simpson’s Index for the site tell you about species richness before and after impact?• Describe and compare the species composition of Site A before and after the impact. How does this analysis compare with the analysis by the Simpson’s Index?
Discussion Questions:• What effect has sheep grazing had on the species composition at this site?• Using this example, explain the limitations of relying only on Simpson’s Index as a determinate for species diversity. What do you suggest to improve the data collection and analysis to determine the site’s diversity?• If you were asked to manage this site for species diversity what would you aim to do?
Shannon-Weiner Index• Another commonly used index is the Shannon-Weiner Diversity Index (H).• Mostly used in freshwater ecology• Based on the question: “How difficult is it to predict correctly the species of the next individual collected?”• The higher the value, between 0 and logS, the higher the species diversity.
Endemism• Australia, as one of the 12 mega-diverse regions on earth, is defined in terms not only of species richness but also in terms of the level of endemism. (species unique to Australia, that exist nowhere else) Number of species % endemic Vascular plants 250,000 85% Mammals 369 82% Birds 825 45% Reptiles 633 89% Frogs 176 93% Invertebrates 193,470 95%
“SAFE” Index• Read the Mathsmasters article in The Age• http://education.theage.com.au/cmspage.php ?intid=147• “Will maths kill the rhino?” by Polster and Ross• Is the “SAFE” Index a good measure of the threat of extinction?• Do you agree with the article?